Thin substrates, such as those used for magnetic disks, require high vacuum processing. This processing generally involves heating of the substrate to a desired temperature and applying different coatings by sputtering or similar physical vapor deposition processes. The high vacuum processes facilitate very high purity coating depositions and the achievement of a variety of properties that are controlled by such parameters as background pressure, coating rate, and substrate temperature. Illustrative is the substrate handling and processing system disclosed in co-pending application Ser. No. 07/763,183, filed Sep. 20, 1991 now U.S. Pat. No. 5,215,420.
Control of substrate temperature in an evacuated environment (i.e. vacuum) is an essential, but difficult task. Typically, heating of a substrate is done by radiation transfer from such devices as quartz lamps. However, normal heat conduction processes work very poorly in the vacuum environment. The atmosphere is not present to supply an ambient environment around the heat sink.
During substrate (or disk) processing, it is also often desirable to lower the substrate temperature. For example, controlled cooling of the substrate may be necessary to achieve a predetermined temperature for a serial coating step, such as chromium, cobalt alloy or carbon layers with magnetic disks. In this instance, the properties of the high hardness, abrasion resistant carbon coatings are enhanced when deposited onto a substrate which is at a relatively low temperature.
Further, cooling of substrates or disks by exposure to the atmosphere while still hot may severely limit the usefulness of such substrates or disks for particular applications. Additionally, uncontrolled cooling and/or cooling in atmosphere could adversely effect coating quality by virtue of the diffusion of different coatings at elevated temperature.
Several prior art techniques have been employed in an attempt to cool the relatively thin substrates during processing. Illustrative is the apparatus disclosed in U.S. Pat. No. 4,909,314. The system disclosed in the noted patent includes a heat exchanging body which is designed and configured to be in contact with the article to be cooled. The system also employs a relatively low conductivity gas, such as argon, to facilitate the heat exchange between the article and the heat exchanging body.
The main disadvantage of such a system is that the act of touching such a relatively thin substrate may do harm to one or more surfaces that have to be maintained in pristine condition. Further, the low mass and the need to handle the substrates only at the edges make them difficult to conductively couple with a heat sink.
Accordingly, it is an object of the invention to provide an improved method for substrate cooling in a vacuum environment which could be employed between process starting steps and not harm the substrate surface of coatings already deposited.
It is a further object of the invention to provide a system for cooling a substrate in a vacuum environment with an enhanced cooling rate so that commercially viable processes could be effected.